diff --git a/src/medley/core.cljc b/src/medley/core.cljc
index 1e9ab08..355f42e 100644
--- a/src/medley/core.cljc
+++ b/src/medley/core.cljc
@@ -658,3 +658,12 @@
   {:added "1.4.0"}
   [x]
   (instance? #?(:clj java.util.regex.Pattern :cljs js/RegExp) x))
+
+(defn index-of
+  "Returns the index of the first occurrence of the item in the sequential
+  collection coll, or -1 if not found."
+  {:added "1.9.0"}
+  [^java.util.List coll item]
+  (if (nil? coll)
+    -1
+    (.indexOf coll item)))
diff --git a/test/medley/core_test.cljc b/test/medley/core_test.cljc
index 0d4981b..f43f6e7 100644
--- a/test/medley/core_test.cljc
+++ b/test/medley/core_test.cljc
@@ -502,3 +502,17 @@
   (is (m/regexp? #"x"))
   (is (not (m/regexp? "x")))
   (is (not (m/regexp? nil))))
+
+(deftest test-index-of
+  (is (= -1 (m/index-of nil :a)))
+  (is (= -1 (m/index-of [] :a)))
+  (is (= -1 (m/index-of '() :a)))
+
+  (is (= -1 (m/index-of  [:a] :b)))
+  (is (= -1 (m/index-of '(:a) :b)))
+
+  (is (= 1 (m/index-of  [:a :b :c :d] :b)))
+  (is (= 2 (m/index-of '(:a :b :c :d) :c)))
+
+  (is (= 1 (m/index-of (range 0 10) 1)))
+  (is (= 1 (m/index-of (map str [:a :b]) ":b"))))